Here is what I use:
http://home.earthlink.net/~wd7s/TU-6B.htm
See it in action here (8877):
http://s900.photobucket.com/albums/ac206/w7ry/8877%20Amplifier/?start=0
And here (3CX800s):
http://s900.photobucket.com/albums/ac206/w7ry/3CX800%20Amplifier/
I use Arco mica compression variable caps for the input and output.
Available at www.rfparts.com
73
Jim W7RY
--------------------------------------------------
From: "w3hvq" <w3hvq@frontiernet.net>
Sent: Wednesday, November 03, 2010 2:37 PM
To: <amps@contesting.com>
Subject: [Amps] My conclusion: Re: Low SWR Input Amps
> Friends,
> The three responses received within a few hours after my posting are
> greatly appreciated. I have decided to scrap the idea of "no input
> tuning" and immediately pursue using a switched-in tapped, tuned circuit
> for each band. I figure on initially setting the tap at the 60 percent
> point from the bottom end of each coil (in the parallel LC circuit). I
> will adjust Q by adjusting the LC ratio so that it will work OK over each
> band. I was especially interested in the amps reflector response number
> 9 which even included a suitable rule-of-thumb input resistor of 90 ohms
> for realistic 4-1000 tests without applying any of the tube's voltages.
> I'm sorry that I do not have time to supply any further information to you
> guys, as I've already put my name in with about 90 others who expect to be
> working the SSCW contest this weekend.
> I can say that I originally built this amplifier in the days when all
> transceivers were of the tube type. That is, all had output tuning and
> loading controls that allowed amplifier's SWR of 2 to 4 to be matched OK.
> There was no consideration ever given to impedance matching within the
> amplifier.
> While I will eventually install tuned circuits for all six HF bands, I
> may omit 160m and 10m for this weekend's activity. Go PVRC!
> Thanks my buddies,
> John, W8OHT
>
>
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